Hi guys, I replaced the engine in my 2005 CNG Civic after the original motor failed due to rod knock. After the swap the car idled fine in park, but as soon as it was put into Reverse or Drive it would stall. I was able to keep the engine from stalling by pressing the gas pedal a bit, and was also able to drive this way, similar to what you would expect from a manual transmission.

I drove it like that for a few weeks before I encountered another engine failure. I decided to get a low mileage motor and transmission, thinking it would solve the stalling problem in addition to replacing the motor. However, after swapping the new motor and transmission in, the motor runs beautifully but still stalls in Reverse and Drive unless I give it a bit of gas.

The thing that really gets me is before the initial motor blew, it would idle fine in Reverse and Drive. Not sure where to start looking for problems as I have no check engine light, but any input would be greatly appreciated.